For some strange reason my Arduino UNO clone board occasionally cause my Mac to reset, when I connect the usb cable. Possibly a power problem in Arduino or the USB hub.

Is it possible to program Arduino UNO with USB/TTL adaptor withouth conncecting the Vcc and GND pins (RX/TX and DTR only.)

  • Which Mac do you have? I'm pretty sure recent Macs have protection on the USB ports - I recently got an error message when I had accidentally shorted Vcc and gnd on an uno. My laptop (2014 15" rMBP running Yosemite) shut off the USB port until I reconnected the USB cable (after fixing the short, of course). – Dennis Munsie May 1 '15 at 0:42
  • It is an iMac 21.5" late 2013 – wizofwor May 1 '15 at 11:09

Is it possible to program Arduino UNO with USB/TTL adaptor without connecting the Vcc and GND pins (RX/TX and DTR only.)

As a minimum you need to add ground as well - even if the Mac is battery powered. Serial port signals are ground referenced so removing the ground would prevent operation.

Operation is possible without deriving Vcc from the USB port, but you will then need to derive Vcc from some other source.

If connecting ground alone causes your Mac to reset you have a serious system problem which may damage your Mac and which possibly may be dangerous to you.

Presumably you are NOT using an external power supply for the UNO.
In case you are: If the power supply for the UNO is AC mains powered it should be connected to the same mains outlet as the Mac. If the programmer powerpack is intended to be grounded but is not powered from a grounded socket AND using a 3 wire mains lead (ie with a ground pin and wire) then it s possible in some cases for the programmer to float at half mains voltage with a high impedance capacitive connection to mains. This is not usually dangerous to people but can cause minor nuisance shocks. It can destroy equipment (ask me how I know :-( .)
If you have a DMM (digital multimeter) set it to an AC voltage range greater than your local mains voltage and measure the AC voltage from a known ground (such as a water tap in most cases) and the programmer power supply (either wire or jack terminal). If you measure a voltage of about 50VAC with 100 VAC mains or about 115 VAC with 230 VAC mains then the power supply MUST be operated with a 3 wire mains cord and grounded power socket OR a ground lead from mains ground to power supply output ground.

If the Mac is battery powered and you have reset problems then something is wrong with connections or signal levels. You may be feeding voltage back onto the USB lines or loading the too heavily or ... ?


If you power the board with an external source of electricity (e.g. a battery), it's possible. But as it can force your Mac to reset, it will possibly damage your battery.

  • At first, I though it was a power problem, like you. But now I'm pretty sure the problem is caused by the CH340G driver. When I check the panic report, last loaded kext is always wch.usb. – wizofwor May 5 '15 at 5:27

It's possible the reboot isn't a hardware issue, short circuiting, but some kind of operating system issue such as a faulty driver, or conflicts... Best to have a look at the Console after a reboot to see if there are any notes here, or try the same Arduino on another Mac or PC.

  • When I check the panic report, last loaded kext is always wch.usb so I assume the problem is caused by this driver. – wizofwor May 5 '15 at 5:21
  • At this point you probably want to look at Apple Support, or a fresh reinstall of the OS and then reimporting your data from a Time Machine backup. – unknowndomain May 5 '15 at 13:32

It is a bit of work, but it is possible to use a couple of optoisolators to build a circuit that will electrically isolate the MCU from the serial adapter.

optoisolator circuit

You should still figure out why your computer resets though, as it may not be related to the Arduino at all (e.g. maybe the cable is bad).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.